Fibroblast growth factor receptor 4 (FGFR-4) is a protein that in humans is encoded by the FGFR-4 gene. This protein is a member of the fibroblast growth factor receptor family, where amino acid sequence was highly conserved between members throughout evolution. FGFR family members 1-4 differ from one another in their ligand affinities and tissue distribution. A full-length representative protein consists of an extracellular region composed of three immunoglobulin-like domains, a single hydrophobic membrane-spanning segment and a cytoplasmic tyrosine kinase domain. The extracellular portion of the protein interacts with fibroblast growth factors, setting in motion a cascade of downstream signals, ultimately influencing mitogenesis and differentiation. The genomic organization of the FGFR-4 gene encompasses 18 exons. Although alternative splicing has been observed, there is no evidence that the C-terminal half of the IgIII domain of this protein varies between three alternate forms, as indicated for FGFR1-3.
Ectopic mineralization, characterized by inappropriate calcium-phosphorus deposition in soft tissue, has been observed in rats treated with an FGFR-1 inhibitor (Brown, A P et al. (2005), Toxicol. Pathol., p. 449-455). This suggests that selective inhibition of FGFR-4 without inhibition of other isoforms of FGFR, including FGFR-1, may be desirable in order to avoid certain toxicities. FGFR-4 preferentially binds fibroblast growth factor 19 (FGF19) and has recently been associated with the progression of certain sarcomas, renal cell cancer, breast cancer, and liver cancer.